When the size of a solid substance is in the order of nanometers (10-9 m), it has been known that properties thereof are varied largely (hereinafter, metal particles having a size of the order of nanometers are referred to as “metal nanoparticles”) as compared with an object having a size enough to be observable (hereinafter referred to as “bulk material”). In particular, it has been known that the melting point of metal particle powder is dramatically lowered when compared with that of the bulk material.
Therefore, a substance which can be melted only at high temperatures in a state of bulk material is expected that metal nanoparticles are melted by heating at relatively low temperatures (up to about 350° C.) and bound to form metal bonding between the substances.
In this technique, it is notable that the metal nanoparticles are melted once to become a bulk material, the bulk material is melted again at the temperature given during a bonding process, and thus peeling cannot occur. That is, when metal originally having a high melting point as a bulk material is utilized for melt bonding as particles having a size of the order of nanometers, the metal can be bonded at low temperatures during the bonding process. At the same time, since the melting point of a bonded portion after the process is near the melting point of the bulk material, a bonding body having high bonding stability can be obtained even when the bonding body is used in an environment at high temperatures. Further, in a substance having a metal species with low ionization tendency, problems of deterioration with age caused by oxidation are unlikely to occur. Accordingly, there is a high demand in applications requiring high reliability.
As a technique disclosed in this field, there has been a literature in which silver oxide microparticles are dispersed in mirystil alcohol, and heated in air to bond substances (see Non-Patent Literature 1). This is a technique in which the alcohol is used to promote properties in which silver oxide is only heated in air to be actively reduced into metal. Further, Patent Literature 1 describes a specific example of this bonding method.
Moreover, Patent Literature 2 discloses that practical bonding strength can be obtained through a bonding method in which particles having different particle diameters are mixed and then heated under pressure.